Preparing a building pad

[Rockbadchild]

Thank you all for your replies, feeling like I'm almost ready to tackle this!


I got confused about the excavator size. I meant to say a 30,000# machine or 15T, so looks like I'm in the ballpark. I think I may rent the excavator for one day, so I'll see how many stumps I can manage to dig out, the rest I can grind or otherwise deal with down the road.

That's interesting about the vibratory plate, I have seen many people use them for more than 1-2" lifts, but from doing some reading, it does seem like the more official rule of thumb is 1" per 1000# force. Oddly enough, my local rental place has a 20" plate and a 1 ton roller and they both put out 3000# eccentric/centrifugal force. Guess I will need to get a larger machine if I want to do higher lifts. Getting proper moisture is going to be a bit tricky as there's no water on-site yet, might have to figure about getting an IBC tote up to the site or wait for some rain.


About the grading around the building, I wasn't too sure what I meant either but after thinking it through, I guess my question is can I do a combination of cut/fill (Option 2)? I think bringing more fill (Option 1) is probably the better way to go to keep water away from the building. It looks like I will have to cut a little swale either way to direct water away from the building, as I'm not at the highest part of the property. Am I thinking about this right? See attached pics below (blue is pole barn)

So my strategy will be to scrape off topsoil, spread and compact ROB up to 6" below highest side of grade (if needed, probably only on left side of building), and then spread and compact 6" crushed rock to match highest side of grade. Finished floor will be 8" above grade.

How much extra material should I add to what I need to figure for compaction?





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as long as all you fill is with external materiel (sand or gravel) any of these is good but don't used your cut materiel as backfill.

 

[EddieWalker]

Come one guys not all deisel plate are created equal



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Plate compactors are not for building up pads. They are for patios and smoothing out gravel or sand. I had good luck renting one to smooth out ruts in a lawn that I created with a skid steer once. Ideally, you want a sheepsfoot compactor, so it mixes the soil while compacting it. The more you build up a pad, the harder it is to get compaction.

On the commercial jobs that I worked on back in the 80's, the Inspector would come out with a box that sent a signal into the dirt, kind of like sonar, that measured compaction. I think Code was something like 98% to pass. If we failed, the dirt was dug out, mixed with dry soil, or mixed with more water, and then put back in lifts. Usually it was a wheel loader that dumped it, a dozer that spread it, and a sheepsfoot compactor that went over it. Those lifts where about two inches, but sometimes, they where a lot less, depending on how far the dozer operator would spread it before the compactor went over it.

For pipe lines, jumpjacks worked, but they are a lot of work. When digging out stumps, I dump a load of dirt in the hole, then when it's up high enough, I start driving over that soil with my front tires and a load of dirt in the bucket. I do this until my tires don't sink anymore, anywhere in the hole. Then build it up to a mound so water sheds away from it. In my opinion, I doubt I'm at 90% compaction, but I'm can live with that for my own place.

 

[Rockbadchild]

Plate compactors are not for building up pads. They are for patios and smoothing out gravel or sand. I had good luck renting one to smooth out ruts in a lawn that I created with a skid steer once. Ideally, you want a sheepsfoot compactor, so it mixes the soil while compacting it. The more you build up a pad, the harder it is to get compaction.

On the commercial jobs that I worked on back in the 80's, the Inspector would come out with a box that sent a signal into the dirt, kind of like sonar, that measured compaction. I think Code was something like 98% to pass. If we failed, the dirt was dug out, mixed with dry soil, or mixed with more water, and then put back in lifts. Usually it was a wheel loader that dumped it, a dozer that spread it, and a sheepsfoot compactor that went over it. Those lifts where about two inches, but sometimes, they where a lot less, depending on how far the dozer operator would spread it before the compactor went over it.

For pipe lines, jumpjacks worked, but they are a lot of work. When digging out stumps, I dump a load of dirt in the hole, then when it's up high enough, I start driving over that soil with my front tires and a load of dirt in the bucket. I do this until my tires don't sink anymore, anywhere in the hole. Then build it up to a mound so water sheds away from it. In my opinion, I doubt I'm at 90% compaction, but I'm can live with that for my own place.

I disagree, I have built many pads for many applications we used diesel heavy diesel vibratory plats to achieve compaction and we did achieve compaction and yes it was tested, is it the most efficient way No but can you absolutely use them, and we did, they both achieve the same result, with a roller you can go with thicker lift and achieve compaction quicker I am not saying otherwise ... We did 4 to 6'' lift for crush gravel 3/4 inch minus and 10 to 12'' for sand with diesel plats . The control test was done with each type of materiel used with a vibratory roller for reference point but after we would used heavy diesel heavy diesel vibratory inside excavations unless there was room to bring a roller, it is very hard to bring a roller inside a some excavation so lots depend on the size of it.

 

[LouNY]

Well I just read through this entire thread.
Lets go back to the first real question what to do with the stumps, being as they are in the building foot print they have to come out.
Once the stumps and all organic material is removed and the filling and compacting begins. In this area compaction is hard to achieve with fills of over 6".
They ideal method is shallow fills, heavy compaction with vibratory rollers including sheeps foot at times.

Even after the "best' filling and compaction there will often be futher settling after a fall and winters season of soil saturation and freezing and thawing.
Ideally the building "pad" would be leveled compacted and left for a season.

I am surprised that your plans didn't include an insulation layer and a vapor barrier under the slab.

 

[rockasawrus]

Well I just read through this entire thread.
Lets go back to the first real question what to do with the stumps, being as they are in the building foot print they have to come out.
Once the stumps and all organic material is removed and the filling and compacting begins. In this area compaction is hard to achieve with fills of over 6".
They ideal method is shallow fills, heavy compaction with vibratory rollers including sheeps foot at times.

Even after the "best' filling and compaction there will often be futher settling after a fall and winters season of soil saturation and freezing and thawing.
Ideally the building "pad" would be leveled compacted and left for a season.

I am surprised that your plans didn't include an insulation layer and a vapor barrier under the slab.

There will be insulation and vapor barrier under the slab.
And yes, the concrete slab won't be poured until some time next year, so I hope it does settle in the interim




Well, I'm back after the first stage of preparing our foundation. Thanks everyone for their comments and suggestions!

I reserved the machines last minute so choices were a bit limited and I ended up with a 20T Linkbelt 160x4, Takeuchi TL8 track loader and a 1.5T roller.

First we dug out the stumps - around 12 in total. All I was able to get was a 36" bucket so I ended up having to dig pretty huge holes; would be curious how different using a frost tooth or smaller bucket would've been. Many of the stumps were 2-3' in diameter and the biggest probably 4'. Holes got filled back in with screened fill in approx 6"-12"lifts and compacted with the bucket.

Next, was figuring out the finished slab height. A few weeks prior to starting, I had checked the elevation with a rotary laser and found that it was 40" difference from the high to low corner; much more than I had eyeballed. I then had a stressful couple days of constantly seconding guessing myself and trying to balance between raising the pad height to accommodate the high back corner and not paying for a ton of a fill.

I ended up bringing in around 180T of screened fill to level the pad. This is what the stone supplier was selling as their version of bank run at $14/ton.
Also got 60T of 3/4" clean rock which will get laid after the piers are done and be part of the radon mitigation system. In retrospect, I should have just waited to order this later.

It was a learning experience for sure, definitely a lot of inefficiency issues and also a bigger roller would've saved so much time. Took about 6 days to do all this work between my girlfriend and I. I thought it would take 3 days.

Now the front corner of the building where the driveway comes up is around 30" above grade, and it will get another 14" on top before finished floor. I have separated topsoil and subsoil from the excavation. Can I use the spoil material fill up to my building grade if I try to get as much organic matter out of it as I can (roots from digging up stumps)?


Still we got it done and we laid out the building for the 24"and 36" Bigfoot piers the engineer specified. Unfortunately, drilling did not go smoothly. The 24" and 36" augers I rented kept getting hung up or catching big rocks. We only got 2 holes done in about 1.5 hours before we snagged the hydraulic hose on the edge of the attachment and hydraulic fluid starting leaking out. I really didn't expect that drilling would be so difficult. At this point, I think I'll have to just rent a mini excavator and just dig each pier out. But I'm a bit worried about getting good compaction when I backfill as I'm going to try to keep the holes small if possible and worried about moving the forms if using a jumping jack compactor. I've got around 25 piers to dig and 2 spread footings. If anyone has any guidance with that, I would appreciated it!


Thanks for reading!

 

[LouNY]

With the "hardpan" soil/subsoil in my area anything loosened while digging a hole or footer is removed and clean fill compacted to the desired height. The subsoil in this area will not compact good enough with mechanical means to not settle after time and freeze/thaw cycles. It can be seen in many building projects, especially parking lots that have had ditching for utilities in a couple of years you can see every ditch in the parking lots from the subsidence of the pavement. And cracks in slabs or foundation walls.

 

[EddieWalker]

Six days isn't bad. I know that a crew can get it done in a day, but that's what they do every day.

I'm very jealous of what you pay for gravel!!!! I paid the same 20 years ago, now it's $60 a ton where I'm at.

 

[rockasawrus]

With the "hardpan" soil/subsoil in my area anything loosened while digging a hole or footer is removed and clean fill compacted to the desired height. The subsoil in this area will not compact good enough with mechanical means to not settle after time and freeze/thaw cycles. It can be seen in many building projects, especially parking lots that have had ditching for utilities in a couple of years you can see every ditch in the parking lots from the subsidence of the pavement. And cracks in slabs or foundation walls.

That's a bummer, looks like I may need to have more material brought in to backfill the forms. Do you think I could get away with using the excavated subsoil for the driveway coming up to the pad? It's going to just be gravel, so even if it sinks here and there I could just bring in more material to fill it until it stabilizes. If not, are there alternatives for cheap road base materials I could ask for?

Six days isn't bad. I know that a crew can get it done in a day, but that's what they do every day.

I'm very jealous of what you pay for gravel!!!! I paid the same 20 years ago, now it's $60 a ton where I'm at.

Good to hear! I was pretty surprised when they told me the price too; it was a fair bit cheaper compared to what another seller was asking for bank run.


I'm still really bummed out about how poorly the auger performed. Part of me is wondering if it had anything to do with the machine/attachment or operator error. Even on full throttle and the auxiliary flow rate set to 1 (100% = 72L/min), and keeping minimal downward pressure on the bit, the bit would get bogged down and stop spinning. That was with some rocks 1-3" in the hole, anything larger I dug out by hand. When the bit would bog down, I would pull it up and drop the soil outside the hole (though a lot would drop back in the hole as it was quite dry). It's also worth mentioning that I caught the hydraulic hoses on the side of the auger attachment and there was a small leak, though I wouldn't expect that to affect performance drastically until a lot of fluid was lost. Based on other videos I've seen of people running augers, the drill will sometimes slow down when encountering resistance, but in our case, the rotation just stopped dead.

Here's a photo of some of the material we were working in.

If anyone has any tips or insight that might mean drilling is still a viable option, I'd love to hear it.

 

[rockasawrus]

For anyone who's curious about how things turned out, we finished our foundation!

Sadly, the events leading up to that were not smooth. I was pretty convinced that drilling was still going to be an option, so I rented a CAT 3000# skidsteer + auger attachment and bits. I needed a 24" and 36" bit for 24" and 36" Bigfoot respectively; unfortunately I called around and all the 36" bits were rented out, so I settled on a 30", hoping I would be able to widen the holes.

Right after the machine arrived and we connected the auger, we noticed that one of the hydraulic hoses was leaking. We lost half the day for them to come out to service it. This combination of machine and attachments performed much better than the previous one. It wasn't easy drilling, but the machine wasn't stalling out at the slightest resistance. The 24" holes went fairly smoothly, but we weren't able to get 36" holes with the 30" bit, which in retrospect should have been obvious. It wasn't too hard to widen the holes at the top by angling the bits, but the bottoms were too narrow.

After we drilled all the holes, that's when reality hit. We pulled the string-lines back and started placing Bigfoot/sonotubes and realized a lot of the holes were not in the right spot. This was probably a combination of operator error but mostly the bit coming off the mark when hitting rocks. In retrospect, other builders I'd seen on YT were drilling in 1) sandier soil with less rocks, and 2) using larger sonotubes (without Bigfoots), so their margin for error was more. Our engineer specified 10" and 12" sonotubes, which made accuracy much more important.

In the end, I ended up re-digging all of the 36" holes with a mini excavator, and probably 25% of the 24" holes. After that, rebar cages went in all the holes. During all this, I talked to two contractors and they said they would recommend using an excavator to dig these. So the lesson learned was to find out what the locals are doing! That being said, most people I talked to were shocked when I told them we were using 36" Bigfoots.

Either way, glad to have made it to this milestone, and here's some photos.

 

[EddieWalker]

Those holes really turned into a lot of work!!!! Sometimes I wish that I had some rocks on my land because I think they look nice, but then I see a thread like yours, and I'm happy that rocks are very rare in my part of East Texas.

I'm curious why you have so many holes? Is there a reason for the close spacing of them?